Kenya has recorded its first case of polio in two years, the World Health Organization said Wednesday.

A 4-month-old girl came down with paralysis on April 30, and then two healthy kids nearby also tested positive for the virus.

But this handful of infections with poliovirus has the potential to set back global efforts to eradicate polio, WHO spokeswoman Sona Bari tells Shots.

"Polio is a virus that spreads silently," she says. "One case represents between 200 and 1,000 people infected. It's the tip of an iceberg."

Kenya hasn't seen a case of wild polio (as opposed to the rare ones linked to vaccination) since July 2011. And now the risk to neighboring countries is very high, Bari says.

"This is a particularly fragile part of the world in terms of immunity," she says. "Overall, Kenya has a robust health care system, but if polio lands in a pocket with low immunity it could spark a large outbreak."

The new case occurred in the largest refugee camp in the world, the Dadaab Refugee Camp in southeast Kenya. About 500,000 people from neighboring countries live there or move in and out of the camp each year.

"There is a lot of travel through this nexus in Africa," Bari says. Viruses can spread rapidly.

"Last time we saw polio in this region, it caused infections in Sudan, Ethiopia, Somalia and even Yemen." Eventually the virus spread as far as Indonesia and paralyzed more than 700 children.

A few weeks ago, Somalia recorded its first wild polio case in more than five years. A 32-month-old girl became paralyzed in the region near Mogadishu.

Many parts of Somalia have not held polio vaccination campaigns since 2009, Global Polio Eradication Initiative said, and the country, in general, has one of the lowest immunization rates in the world.

Genetic analysis suggests that the poliovirus in Somalia came from Nigeria, which is more than 3,000 miles away. It's still unknown if the Somalia case is connected with the ones in Kenya. But the international health community has responded quickly to contain both outbreaks.

"Fortunately, we're prepared for these things," Bari says. Vaccinations campaigns will start in Kenya this Sunday. In Somalia, they've already immunized about 400,000 children. "About 1 million children will get vaccinated in eastern Kenya," she says.

Such rapid responses are critical if the WHO and other foundations hope to reach their target of eradicating polio by 2018 a goal that health leaders said would cost about $5.5 billion.

Polio is currently endemic in just three countries: Afghanistan, Pakistan and Nigeria. There were only 223 cases recorded worldwide in 2012 and so far, just 34 in 2013.More than half of the cases occurred in Nigeria.